loosen source_gen and build version constraints

Author: FrankenApps

embed/pubspec.yaml

@@ -9,8 +9,8 @@ environment:
 dependencies:
   analyzer: '>=7.4.0 <9.0.0'
   embed_annotation: ^1.2.1
-  build: ^3.0.0
-  source_gen: ^3.1.0
+  build: '>=3.0.0 <5.0.0'
+  source_gen: '>=3.1.0 <5.0.0'
   path: ^1.9.1
   yaml: ^3.1.3
   recase: ^4.1.0